The present invention generally relates to a communication device and, more particularly, to a heat radiating structure for dissipating heat from a pyrogenic element enclosed within a housing.
In conventional electronic devices such as mobile communication devices, there is such a mobile communication device including a heat radiating structure for dissipating heat generated from a built-in pyrogenic element as shown in FIG. 17. FIG. 17 illustrates a sectioned structural diagram showing an important structure of the conventional mobile communication device disclosed in the Japanese Laid-open Patent Publication No. 11-204970. In this figure, reference numeral 1 represents a heat generating element (hereinafter referred to as a pyrogenic element), reference numeral 2 represents a printed substrate on which a communication circuitry including the pyrogenic element 1 is mounted, reference numeral 4 represents a housing for accommodating the printed substrate, and reference numeral 10 represents a heat radiating plate.
The air has a low thermal conductivity, say, 0.026 W/mK and, accordingly, where a air layer exits between the pyrogenic element 1 and the housing 4, thermal resistance between the pyrogenic element 1 and the housing 4 is high, the temperature difference is large, and there is a problem that the pyrogenic element 1 tends to be heated to a high temperature. For this reason, a heat radiating plate 10 made of aluminum (having a thermal conductivity of 230 W/mK) or carbon (having a thermal conductivity of 500 to 800 W/mK) has one end held in tight contact with the pyrogenic element 1, and the opposite end mounted to the inner wall of the housing 4 that is low in temperature.
With the above construction, the thermal resistance from the pyrogenic element 1 to the housing 4 is reduced and the element temperature can be lowered.
However, thermal limiting conditions of the mobile communication device include not only lowering of the element temperature, but also there is a thermal limiting condition between the element temperature and the housing temperature. By way of example, in the case of a personal computer there is no problem even if the temperature of the bottom becomes high, but the mobile telephone has to have the housing temperature limited since the instrument is often brought into contact with the user""s hand and face.
With the heat radiating structure shown in FIG. 17, there is a problem that since the heat liberated from the pyrogenic element 1 is locally conducted to the housing 4 to which that end of the heat radiating plate 10 is mounted, a surface temperature of the housing 4 tends to become locally high.
FIG. 18 illustrates a sectioned structural diagram showing an important structure of another electronic equipment (an optical receiver) having a heat radiating function disclosed in the Japanese Laid-open Patent Publication No. 10-41678. In this figure, reference numeral 1 represents a heat generating circuit element (hereinafter referred to as a pyrogenic element) such as an amplifying circuit, a demodulating circuit or the like, reference numeral 2 represents a printed substrate on which the pyrogenic element 1 is mounted, reference numeral 3 represents a shield casing for shielding the pyrogenic element 1, reference numeral 4 represents a housing, reference numerals 11 and 12 represent respective heat conductive sheets (having a thermal conductivity of 1 W/mK) of a silicone system or the like disposed in an air layer between the pyrogenic element 1 and the shield casing 3 and in an air layer between the shield casing 3 and the housing 4.
Even in such construction, although as is the case with the previously described prior art, the thermal resistance between the pyrogenic element 1 and the housing 4 becomes low, the temperature difference becomes small and the element temperature can therefore be lowered, there is a problem that the surface temperature of the housing tends to be locally high since heat liberated from the element is locally conducted to an inner wall of the housing 4 to which one end of the heat conductive sheet 12 is mounted.
FIG. 19 illustrates a sectioned structural diagram showing an important structure of another electronic equipment having a heat radiating function disclosed in the Japanese Laid-open Patent Publication No. 63-124598. In this figure, reference numeral 1 represents an integrated circuit which is a heat generating circuit element (hereinafter referred to as a pyrogenic element). Reference numeral 2 represents a printed substrate on which the pyrogenic element 1 is mounted, reference numeral 3 represents a shield casing provided on an undersurface of the print substrate 2 for shielding the printed substrate 2, and reference numeral 13 represents a thermally conductive insulating body filled between the undersurface of the printed substrate 2 and the shield casing 3.
Although even in such construction heat liberated from the pyrogenic element 1 can be radiated, since in this prior art, the thermally conductive electrically insulating body 13 is mounted through the printed substrate, the temperature increase of an element of a thermal resistance component of the printed substrate cannot be reduced. Also, since for the thermally conductive electrically insulating body 13, a thermally conductive material having a thermal conductivity that is relatively low as compared with that of a metallic material such as aluminum or the like ({fraction (1/100)} to {fraction (1/200)} of the thermal conductivity of aluminum) is employed, a relatively large volume of the thermally conductive material is needed to sufficiently dissipate the heat, resulting in the electronic equipment that is heavy.
FIG. 20 illustrates a sectioned structural diagram showing an important structure of another electronic equipment (a printed circuit board device) having a heat radiating function disclosed in the Japanese Laid-open Utility Model Publication No. 3-8496. In this figure, reference numeral 1 represents a semiconductor component which is a heat generating circuit element (hereinafter referred to as a pyrogenic element). Reference numeral 2 represents a printed circuit board on which the pyrogenic element 1 is mounted, and reference numeral 3 represents a shielding plate fitted to the printed circuit board 2 for electromagnetically shielding it from other printed circuit boards. Reference numeral 14 represents an L-shaped metal piece provided between the pyrogenic element 1 and the shielding plate 3.
Although even in such construction heat liberated from the pyrogenic element 1 can be radiated through the shielding plate 3, there is a problem in this prior art that since the metallic material is mounted in the vicinity of the semiconductor component, no electric characteristic can be warranted and the L-shaped metal piece is unable to diffuse heat sufficiently within a plane of the shielding plate 3.
The present invention has been aimed at solving the above discussed problems and has its object to provide a communication device in which the temperature of the pyrogenic element is reduced efficiently and the surface temperature of the housing can be lowered.
A first communication device according to the present invention includes a communication circuit mounted on a printed substrate and having a heat generating element; a shield casing covering the communication circuit and shielding electromagnetic waves; a housing for accommodating the printed substrate having the shield casing and the communication circuit mounted thereon; a heat diffusing member mounted along an inner wall of the shield casing for diffusing heat in a planar direction; and a heat insulating layer disposed between the shield casing and an inner wall of the housing. According to this, local increase of the temperature of the housing to a high temperature can be suppressed and, also, the temperature of the pyrogenic element can be efficiently lowered.
A second communication device according to the present invention includes, in the above described first communication device, a electrically insulating, thermally conductive member disposed between the heat diffusing member and the heat generating element. According to this, not only can the electric characteristic warranted, but also a high cooling effect can be obtained even though a small volume of heat conductive member is inserted, resulting in efficient lowering of the temperature of the pyrogenic element.
A third communication device according to the present invention includes a communication circuit mounted on a printed substrate and having a heat generating element; a metal type shield casing covering the communication circuit and shielding electromagnetic waves; an electrically insulating, thermally conductive member disposed between the metal type shield casing and the heat generating element; a housing for accommodating the printed substrate having the shield casing and the communication circuit mounted thereon; a heat insulating layer disposed between the shield casing and an inner wall of the housing. According to this, local increase of the temperature of the housing to a high temperature can be suppressed and, also, the temperature of the pyrogenic element can be efficiently lowered.
A fourth communication device according to the present invention includes a communication circuit mounted on a printed substrate and having a heat generating element; a shield casing covering the communication circuit and shielding electromagnetic waves; a housing for accommodating the printed substrate having the shield casing and the communication circuit mounted thereon; a heat diffusing member mounted along an outwall of the shield casing for diffusing heat in a planar direction; and a heat insulating layer disposed between the heat diffusing member and an inner wall of the housing. According to this, local increase of the temperature of the housing to a high temperature can be suppressed and, also, the temperature of the pyrogenic element can be efficiently lowered. Also, since a large mounting area for the heat diffusing member can be secured, it is particularly effective for lowering the housing temperature.
A fifth communication device according to the present invention includes, in the fourth communication device, an electrically insulating, thermally conductive member disposed between an inner wall of the shield casing and the heat generating element. According to this, not only can the electric characteristic warranted, but also a high cooling effect can be obtained even though a small volume of heat conductive member is inserted, resulting in efficient lowering of the temperature of the pyrogenic element.
Sixth to eighth communication devices according to the present invention are such that in any of the first, third and fourth communication devices, a heat diffusing member for diffusing heat in a planar direction is mounted on an inner or outer wall of the housing. According to this, the housing temperature can be equalized further and lowering of the housing temperature is possible.
Ninth to eleventh communication devices according to the present invention are such that in any of the sixth to eighth communication devices, the heat diffusing member provided on the housing inner wall is of a shape in which a portion thereof confronting the heat generating element within the shield casing or a portion thereof confronting a component provided externally on the shield casing protrudes towards the shield casing. According to this, there is an effect that the housing will not be heated partially.
Twelfth to fourteenth communication device according to the present invention are such that in any one of the first, third and fourth communication devices, a heat equalizing member is provided on an outer wall of the shield casing excluding a location where a component provided externally of the shield casing, or an inner wall of the housing excluding an inner wall portion of the housing confronting the above described component. According to this, there is an effect that the housing will not be heated partially.
Fifteenth to seventeenth communication devices according to the present invention are such that in any of the first, third and fourth communication devices, the housing is of a shape wherein a portion thereof confronting the heat generating element within the shield casing, or a portion thereof confronting a component provided externally of the shield casing protrudes outwardly. According to this, there is an effect that the housing will not be heated partially.
Eighteenth to twentieth communication devices according to the present invention are such that in any one of the first, third and fourth communication devices, the housing is of a shape wherein a portion thereof confronting the heat generating element within the shield casing, or a portion thereof confronting a component provided externally of the shield casing protrudes inwardly. According to this, even though the temperature of the housing increases locally, a human body would hardly contact that portion where the temperature has increased, and it is possible to avoid any inconvenience brought about increase of the temperature.